fix(rivetkit): fix BigInt serialization in inspector workflow history and state deserialization

[abcxff]

Description

Please include a summary of the changes and the related issue. Please also include relevant motivation and context.

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

Please describe the tests that you ran to verify your changes.

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[railway-app]

🚅 Deployed to the rivet-pr-5058 environment in rivet-frontend

Service	Status	Web	Updated (UTC)
website	😴 Sleeping (View Logs)	Web	May 19, 2026 at 8:28 pm
frontend-cloud	😴 Sleeping (View Logs)	Web	May 19, 2026 at 8:27 pm
frontend-inspector	❌ Build Failed (View Logs)	Web	May 19, 2026 at 8:20 pm
kitchen-sink	❌ Build Failed (View Logs)	Web	May 19, 2026 at 8:19 pm
ladle	✅ Success (View Logs)	Web	May 19, 2026 at 8:19 pm
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[abcxff]

• fix(rivetkit): wire CancellationToken through waitForNamesAvailable to eliminate KV busy-polling #5063 : 2 dependent PRs (#5050 , #5065 )
• fix(rivetkit): fix BigInt serialization in inspector workflow history and state deserialization #5058 👈 (View in Graphite)
• fix(workflow-engine): only commit step state after success #5010 : 1 other dependent PR (#5052 )
• fix(rivetkit): bind methods through createWriteThroughProxy #4987
• fix(rivetkit): remove client-side connection request size check #5057
• main

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[claude]

Code Review — fix(rivetkit): fix BigInt serialization in inspector workflow history and state deserialization

Overview

This PR fixes two distinct BigInt-related bugs in the RivetKit TypeScript runtime:

1. State deserialization (decodeValue): was calling decodeCborJsonCompat, which silently coerces safe-integer BigInts to Numbers, corrupting stored BigInt actor state.
2. Inspector workflow history (serializeWorkflowHistoryForJson): was returning raw BigInt values that caused JSON.stringify to throw TypeError: Do not know how to serialize a BigInt.

---

Correctness

decodeValue change — correct.
Switching from decodeCborJsonCompat to decodeCborCompat is the right fix. encodeCborCompat wraps BigInts as bigint-tagged tuples, and decodeCborCompat faithfully revives them. The old decodeCborJsonCompat path was silently losing type information for any user state that stored BigInt values.

serializeWorkflowHistoryForJson change — correct with a known caveat.
Wrapping with jsonSafe() prevents the JSON serialization crash. However, toHttpJsonCompatible (called by jsonSafe) converts BigInts to Number, which is lossy for values outside the safe integer range. For epoch-ms timestamps this is fine in practice, but large integer IDs or counters stored as BigInt would silently lose precision. The TODO comment acknowledges this and CBOR encoding is the correct long-term fix.

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Issues

1. Accidental ext/test workspace inclusion — should be reverted

pnpm-workspace.yaml adds ext/* and pnpm-lock.yaml gains an ext/test entry referencing @hono/node-server, @rivetkit/engine-cli, @rivetkit/rivetkit-napi, and rivetkit. The ext/ directory does not exist in the repository — this appears to be a local test harness used during development that was accidentally committed. This will cause pnpm install to warn or fail for other contributors and should be reverted before merge.

2. No regression tests added

Both bugs are straightforward to reproduce and guard against:

• A driver test that stores a BigInt actor state value, hard-crashes the actor, and asserts the revived state preserves the BigInt type (not a Number).
• A unit test that calls serializeWorkflowHistoryForJson with a history containing BigInt fields and confirms no serialization error is thrown.

Without these, the bugs could silently regress.

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Minor Notes

• The TODO comment (// TODO: Switch inspector routes to CBOR encoding) is good to have; make sure it lands in a tracked issue or .agent/todo/ entry so it does not get lost.
• Removing the now-unused decodeCborJsonCompat import is clean.

[abcxff]

Merge activity

• May 19, 8:06 PM UTC: A user started a stack merge that includes this pull request via Graphite.
• May 19, 8:08 PM UTC: The Graphite merge of this pull request was cancelled.